This invention relates generally to the manner of operation of a pyrolysis type furnace for removal of various organic contaminants from metal parts and more particularly to a novel manner for said furnace operation which provides superior heating efficiency.
In our earlier issued U.S. Pat. No. 4,970,969 there is described a novel batch type pyrolysis furnace for volatilizing and burning organic material from a metal part to which said organic material is bonded. This furnace apparatus employs a main combustion chamber operating at negative chamber pressure which is heated with an adjustable heating rate burner to directly heat air ducted into said main combustion chamber by convection heat transfer. A supplemental combustion chamber in open communication with said main combustion chamber and vented to the atmosphere contains an auxiliary burner to complete combustion of the volatilized organic contaminants being transported from the main combustion chamber. A single temperature sensing means is disposed within said main combustion chamber together with water spray means responsive to said temperature sensing means for operative cooperation with said adjustable heating rate burner to regulate operating temperatures within said main combustion chamber in accordance with a preselected heating schedule. Control of the furnace operation includes programmable temperature control means to maintain continuous operation of said adjustable heating rate burner with (i) a normal full supply of fuel necessary to maintain full combustion in the presence of excess oxygen during a major portion of the pyrolysis cycle, said excess oxygen being relative to the amount required to burn the fuel in said burner, and (ii) a diminished supply of fuel sufficient to maintain fuel-starved combustion during the final portion of the pyrolysis cycle, also in the presence of excess oxygen. The entire contents of my earlier issued patent are hereby specifically incorporated into the present application since the present invention provides a superior manner of operating this same type pyrolysis furnace.
Said prior art method of heating air solely by convection in this type furnace is subject to serious drawbacks including a relatively low rate of heat transfer as well as an inherent requirement for air movement. These heating characteristics result in longer startup and cool down periods for the pyrolysis cycle. Understandably, such extended furnace operation to complete the pyrolysis cycle further increases both fuel and still other operating costs. Heating solely with convection heating means can also increase furnace equipment costs by utilization of recirculating fans to improve air movement during the pyrolysis cycle. Having the present pyrolysis cycle being carried out entirely with convection heating results in still further drawbacks attributable to uneven heating taking place in the main combustion chamber. The contaminated metal parts in the main combustion chamber are heated non-uniformly resulting in damaged products while uneven heating also produces cold spots in the furnace enclosure with stratification of warm air at roof level further wasting fuel efficiency.
It is an important object of the present invention, therefore, to provide a more effective means to remove organic contaminants from metal parts in a pyrolysis furnace.
It is another important object of the present invention to provide novel heating means in a pyrolysis furnace exhibiting superior heating efficiency.
Still another important object of the present is to provide novel heating means in a batch type pyrolysis furnace for energy savings and shorter time cycles.
Still another important object of the present invention is to provide a novel method for heating in a pyrolysis furnace.
These and still further objects of the present invention will become more apparent upon considering the following more detailed description of the present invention.
It has been discovered, surprisingly, that removal of organic contaminants from metal parts in a pyrolysis furnace can be carried out more effectively with combined radiant and convection heating in a particular manner during the pyrolysis cycle. More particularly, the processing procedure of the present invention employs a pyrolysis furnace having a main combustion chamber employing an adjustable heating rate burner adapted to supply both convection and radiant heating energy to directly heat air ducted into said main combustion chamber for passage of the volatilized organic contaminants into a supplemental combustion chamber in open communication with said main combustion chamber and vented to the atmosphere which further contains an auxiliary burner. In said operating procedure, the main combustion chamber is operated with a single temperature sensing means in combination with control means including programmable temperature control means to maintain continuous operation of said adjustable heating rate burner with (i) a normal fuel supply necessary to maintain full combustion of said organic contaminants in the presence of excess oxygen during a major portion of the pyrolysis cycle, said excess oxygen being relative to the amount required to burn the fuel in said burner, and (ii) a diminished supply of fuel sufficient to maintain fuel-starved combustion during the final portion of the pyrolysis cycle, also in the presence of excess oxygen, while further activating a water spray within said main combustion chamber responsive to said temperature sensing means for operative cooperation with said adjustable heating rate burner to regulate operating temperature within said combustion chamber in accordance with a preselected heating schedule, and employing said auxiliary burner to complete the combustion of the volatilized organic contaminants being transported from the main combustion chamber within said supplemental combustion chamber. A suitable adjustable heating rate burner enabling the desired purpose can simply feature a radiant tube extension protruding from the front end of said burner which further includes multiple openings along the tube length. Said modified burner assembly can be easily positioned beneath the cart member containing the contaminated metal parts being processed within the main combustion chamber. Employing such heating means enables the modified gas burner to fire directly into the length of the radiant tube extension for its rapid heating as the radiant energy source while simultaneously supplying convection heating with flames emerging evenly out the tube openings. The illustrated burner construction has been found to enable a 50% improvement for the present operating procedure in rapid heat-up and cool-down during shortened cycle times accompanied by a 20% fuel savings.